May J M
Department of Medicin, 736 Medical Research Building II, Vanderbilt University School of Medicine, Nashville, TN 37232-6303, USA. james.may@ mcmail.vanderbilt.edu
Front Biosci. 1998 Jan 1;3:d1-10. doi: 10.2741/a262.
Ascorbic acid, or vitamin C, is an important antioxidant in plasma, where it consumes oxygen free radicals and helps to preserve alpha-tocopherol (vitamin E) in lipoproteins. Erythrocytes, as the most plentiful cell in blood, help to preserve ascorbate in the blood plasma. In contrast to nucleated cells, which avidly concentrate ascorbate, the erythrocyte ascorbate concentration is the same as that in plasma. Erythrocytes nonetheless have a high capacity to regenerate the vitamin from its two electron-oxidized form, dehydroascorbic acid (DHA). DHA is rapidly taken up by these cells on the abundant glucose transport protein, GLUT1. Intracellular DHA is rapidly reduced to ascorbate by GSH in a direct chemical reaction, although enzyme-dependent mechanisms involving both glutaredoxin and thioredoxin reductase have also been demonstrated. Ascorbate, which carries a negative charge at physiologic pH, enters and leaves the cells slowly. Nonetheless, this slow release of ascorbate from erythrocytes can preserve both the plasma concentration of the vitamin, and prevent oxidation of alpha-tocopherol in low-density lipoprotein. In addition, intracellular ascorbate can spare and possibly recycle alpha-tocopherol in the erythrocyte membrane. In turn, alpha-tocopherol protects the cell membrane from lipid peroxidation. The ability of erythrocytes to recycle ascorbate, coupled with the ability of ascorbate to protect alpha-tocopherol in the cell membrane and in lipoproteins, provides a potentially important mechanism for preventing lipid peroxidative damage in areas of inflammation in the vascular bed, such as those involved with atherosclerosis.
抗坏血酸，即维生素C，是血浆中的一种重要抗氧化剂，它消耗氧自由基并有助于维持脂蛋白中的α-生育酚（维生素E）。红细胞作为血液中最丰富的细胞，有助于维持血浆中的抗坏血酸盐。与大量摄取抗坏血酸盐的有核细胞不同，红细胞中的抗坏血酸浓度与血浆中的相同。然而，红细胞具有从其二电子氧化形式脱氢抗坏血酸（DHA）再生维生素的高能力。DHA通过丰富的葡萄糖转运蛋白GLUT1迅速被这些细胞摄取。细胞内的DHA通过谷胱甘肽（GSH）在直接化学反应中迅速还原为抗坏血酸，尽管也已证明涉及谷氧还蛋白和硫氧还蛋白还原酶的酶依赖性机制。在生理pH下带负电荷的抗坏血酸缓慢进出细胞。尽管如此，抗坏血酸从红细胞中的这种缓慢释放可以维持维生素的血浆浓度，并防止低密度脂蛋白中的α-生育酚氧化。此外，细胞内的抗坏血酸可以节省并可能循环利用红细胞膜中的α-生育酚。反过来，α-生育酚保护细胞膜免受脂质过氧化。红细胞循环利用抗坏血酸的能力，以及抗坏血酸保护细胞膜和脂蛋白中α-生育酚的能力，为预防血管床炎症区域（如动脉粥样硬化涉及的区域）的脂质过氧化损伤提供了一种潜在的重要机制。
